1. Field of the Invention
The present invention is generally directed to implantable devices, and more particularly, to an implantable cochlear access device.
2. Related Art
Hearing loss, which may be due to many different causes, is generally of two types, conductive and sensorineural. In some cases, an individual may have hearing loss of both types. In many people who are profoundly deaf, however, the reason for their deafness is sensorineural hearing loss. Sensorineural hearing loss occurs when there is damage to the inner ear, or to the nerve pathways from the inner ear to the brain. As such, those suffering from sensorineural hearing loss are thus unable to derive suitable benefit from conventional acoustic hearing aid. As a result, hearing prostheses that deliver electrical stimulation to nerve cells of the recipient's auditory system have been developed to provide persons having sensorineural hearing loss with the ability to perceive sound. Such electrically-stimulating hearing prostheses deliver electrical stimulation to nerve cells of the recipient's auditory system.
As used herein, the recipient's auditory system includes all sensory system components used to perceive a sound signal, such as hearing sensation receptors, neural pathways, including the auditory nerve and spiral ganglion, and parts of the brain used to sense sounds. Electrically-stimulating hearing prostheses include, for example, auditory brain stimulators and cochlear™ prostheses (commonly referred to as cochlear™ prosthetic devices, cochlear™ implants, cochlear™ devices, and the like; simply “cochlear implants” herein.)
Most sensorineural hearing loss is due to the absence or destruction of the cochlea hair cells which transduce acoustic signals into nerve impulses. It is for this purpose that cochlear implants have been developed. Cochlear implants use direct electrical stimulation of auditory nerve cells to bypass absent or defective hair cells that normally transduce acoustic vibrations into neural activity. Such devices generally use an electrode array implanted in the cochlea so that the electrodes may differentially activate auditory neurons that normally encode differential pitches of sound.
Auditory brain stimulators are used to treat a smaller number of recipients with bilateral degeneration of the auditory nerve. For such recipients, the auditory brain stimulator provides stimulation of the cochlear nucleus in the brainstem, typically with a planar electrode array; that is, an electrode array in which the electrode contacts are disposed on a two dimensional surface that can be positioned proximal to the brainstem.
In contrast to sensorineural hearing loss which results from damage to the inner ear, conductive hearing loss occurs when the normal mechanical pathways used to provide sound to hair cells in the cochlea are impeded, for example, by damage to the ossicular chain or to the ear canal. Individuals who suffer from conductive hearing loss typically have some form of residual hearing because the hair cells in the cochlea are undamaged. Such individuals are typically not candidates for a cochlear implant due to the irreversible nature of the cochlear implant. Specifically, insertion of the electrode array into a recipient's cochlea exposes the recipient to the risk of destruction of the majority of the hair cells within the cochlea, resulting in the loss of all residual hearing by the recipient.
As a result, individuals suffering from conductive hearing loss typically receive an acoustic hearing aid. Unfortunately, not all individuals who suffer from conductive hearing loss are able to derive suitable benefit from hearing aids. For example, some individuals are prone to chronic inflammation or infection of the ear canal and cannot wear hearing aids. Similarly, hearing aids are typically unsuitable for individuals who have malformed, damaged or absent outer ears, ear canals and/or ossicular chains.
Those individuals who suffer conductive hearing loss, but cannot derive suitable benefit from hearing aids may benefit from devices which simulate natural hearing by generating mechanical motion of the cochlear fluid (perilymph) without the need for operable outer and middle ears. Some such devices, sometimes referred to mechanical stimulators herein, have one or more components in direct contact with the perilymph so that a propagating wave may be generated within the perilymph. The propagating wave excites the cochlea hair cells and thereby evokes a hearing percept.